And to think, Kurama and Hiei were supposed to be a gay couple. But, of course, the publishers wouldn't allow it, leading to Mukuro being brought in to give Hiei an ending, considering he was supposed to die early in the season. Fangirls complained and demanded he be brought back though.

I should probably elaborate (sorry, major nerd here)
Sayako: Is behind the demon attacking the Togoro brother's dojo, and behind thier defeat of the demon and subsequent turning into demons themselves. Fuses thier souls to a piece of paper which he owns. He then runs the dark tournement with the purpose of making bets on who would win or lose. Purposely drives Sensui insane by allowing him to aquire chapter black. May have been responsible for knocking that kids ball into traffic (you know the one).

Eldar Togoro cannot walk much under his own power. Usually, he rides around on his brother's back. When his brother is dead, he orafice invades a human and controls him. He mentions it's not the first time. He really, really, likes redheads like Kurama, and tries to make him his next host. Which is what Karasu tried to do, so I have reasonable suspicions that Eldar Togoro was using Karasu as a meat puppet for upwards of 20 years or whatever.

Togoro brothers- big muscley guy and creepy immortal shoulder monkey (the eldar one cannot seen to walk much under his own power)
Karasu- Creepy guy modeled after jakotsu from Inuyasha, Deidara from Naruto and a super sayan. Tried to rape Kurama while causing as much physical and mental agony as possible. May have just been a meat puppet for the elder Togoro brother though.
Gonzo- Man who tortured Yukina to make her cry
Sayako- The man behind EVERYTHING in Yu Yu Hakusho, and not in a good way

well thank you for that lol I remember the togoro brothers, they were in the tournament thing and the shoulder monkey thing got fly swatted by kuwabara but he didnt really die or something and came up in a later season or something, and I might know Sayako if he's the guy that was a spirit detective before Yusuke and he was the main villain after the tournament

Yusuke- Spirit detective, the one one in green
Kuwabara- the big one with red hair, assistant
Boton- tall blue haired girl, the grim reaper
Yukina- short blue haired girl, kidnapped ice maiden who cries jewels like the rest of her one gender race
Hiei- Short, black cloak. Secretly Yukina's sister, but being male he was thrown off a mountain
Kurama- 700 year old fox demon thief, temporarily in a human body, long red hair
Koenma- Enma's son (Enma is god in japanese mythos)

These are some of the main good characters. Do you want the bad characters as well?

Half of the characters from street fighter show up at Genkai's tourtement. Karasu is supposed to be a reference to DBZ, as well as Jakatsu from Inuyasha and Deidara from Naruto. Not to mention the author of Yu Yu Hakusho is married to the writer of Sailor Moon. I also think the writer liked the Inuyasha Sesshomaru pairing and modeled Yoko Kurama after what thier child would look like, but made him a fox.